Because the value if things is subjective. Your friend needs to read some Austrian economists. There is no intrinsic or extrinsic value, things are valued because of you, your needs and feelings in your location at your given time, pure and simple. This is reflected in the price market.

Why is still being valued and not suddenly abandoned? Because its useful to them the way it is. Anything backed by a gov or company will last as long as that gov/company, i have seen more of those disappear in my lifetime.

Should you even trust gov / company? All they give you is a promise that can be broken at any time. Bitcoin has established rules executed by computer code. One of them being the 21 million thing, and the other how hard is to change those rules. When people learn more about it they give it more value, it doesn't depend on you or your friend at all. And no, a value given by a collective isn't inferior to a gov decree or company product, quite the opposite in fact. Bitcoin will still work even if India disappears and becomes a colony again. Do you get it? How strong it is? It is BORDERless, BANKless and STATEless... This is the first time in human history that we have a true world coin. Rupees are useless here, let me tell you. It will be VERY hard to find someone to exchange that exotic money and probably at outrageous rates.

Why are there communities across the world accepting bitcoin? For example tourists don't need to deal with exchanging money anymore... Isn't it valuable to them? That is why. Start summing those that consider it valuable for whatever reason and those who don't. You get the market price, but even that is not the complete picture, as many coins are not in the market either, many are simply saving them for the future, because THEY (not your GOV, not a Company) think its worth keeping.